Electrophoretic display method and device

ABSTRACT

An electrophoretic display device includes a first substrate, first and second driving electrodes arranged on the first substrate, a second substrate arranged in an opposing relation to the first substrate and a third driving electrode arranged on the second substrate. A transparent dielectric liquid is filled between the first substrate and the second substrate, and a plurality of migratory particles are dispersed in the transparent dielectric liquid. A barrier is disposed on a surface of the third driving electrode arranged on the second substrate and is situated in an opposing relation to a boundary between the first driving electrode and the second driving electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophoretic display method anddevice in which charged migratory particles are migrated for display ofan image.

2. Description of the Related Art

Recently, with rapid development of information equipment, the amount ofdata included in various kinds of information has increased more andmore, and output of the information has been made in various forms.Generally, information is outputted in two primary ways, i.e.,display-screen representation using a CRT or a liquid crystal, andhard-copy representation on paper using a printer or the like. In thedisplay-screen representation, increasing needs exist for a displaydevice that has low power consumption and is thin. Above all, a liquidcrystal display has been actively developed and commercialized as adisplay device adaptable for such needs.

However, a current liquid crystal display has problems, which are notyet overcome to a satisfactory level, in that characters displayed on ascreen become hard to perceive depending on the angle of viewing thescreen and the presence of reflected light, and a burden is imposed on aviewer's visual organ due to, e.g., flickering and low luminance of alight source. Also, the display-screen representation using a CRT canprovide the contrast and luminance at a satisfactory high level ascompared with the case of using a liquid crystal display, but itaccompanies flickering, etc. and hence also cannot be regarded as havinga sufficient display quality as compared with the hard-copyrepresentation described below. Additionally, the display-screenrepresentation using a CRT entails a large and heavy body, and istherefore very poor in portability.

Meanwhile, at the beginning of the electronization era, it was thoughtthat the hard-copy representation would no longer be required with theprogress of electronization of information. In practice, however, agreat deal of information is still outputted in the form of hard copies.The reasons are as follows. When information is displayed using adisplay unit, there occurs not only the above-mentioned problems withregard to display quality, but also another problem that a resolutionachieved by the display-screen representation is generally about 120 dpiat maximum, which is fairly lower than that in the case of printing outinformation on paper (usually not lower than 300 dpi). Accordingly, thedisplay-screen representation imposes a greater burden on a viewer'svisual organ than the hard-copy representation. As a result, althoughinformation can be confirmed on a display screen, the information isoften outputted in the form of hard copies. Another major reason why thehard-copy representation is utilized in spite of a capability ofdisplaying information on a display screen, is that, unlike thedisplay-screen representation, hard copies of information can bearranged side by side in large number without being restricted by adisplay size defining a display area, and they can be rearranged orchecked in order with no need of complicated device operations.Furthermore, the hard-copy representation requires no energy for holdinginformation in a represented state, and has superior portabilityenabling information to be read or checked in any place and at any timeunless the amount of information is extremely large.

Thus, the hard-copy representation has various merits over thedisplay-screen representation so long as moving images or frequentrewriting is not needed, but it is disadvantageous in consuming a greatdeal of paper. In recent years, therefore, a rewritable recording medium(i.e., a recording medium that enables an image to be displayed in manyrecording and erasing cycles with high viewability, but does not requireenergy for holding the image in a displayed state) has been activelydeveloped. Such a third rewritable display system taking over superiorcharacteristics of hard copies is herein called a paper-like display.

Requirements of the paper-like display are, for example, that it isrewritable, requires no or a sufficiently small amount of energy forholding an image in a displayed state (memory character), has superiorportability, and has a high display quality. At present, one example ofa display system, which can be regarded as the paper-like display, is areversible display medium employing an organic low-molecular andhigh-molecular resin matrix and being able to record or erase an imageby a thermal printer head (e.g., see Japanese Patent Laid-Open Nos.55-154198 and 57-82086). Such a matrix is employed in display portionsof some prepaid cards, but still has problems that the contrast is notso high and the number of times at which an image can be recorded anderased repeatedly is relatively small, i.e., on the order of 150 to 500.

As another display system capable of being utilized as the paper-likedisplay, there is known an electrophoretic display device (U.S. Pat. No.3,612,758) invented by Harold D. Lees, et al. Also, Japanese PatentLaid-Open No. 9-185087 discloses an electrophoretic display device. Sucha display device comprises a disperse system wherein charged migratoryparticles are dispersed in a dielectric liquid, and a pair of electrodesis arranged in an opposing relation with the disperse system situatedbetween the electrodes. By applying a voltage to the disperse systemthrough the electrodes, charged migratory particles are attracted underelectrostatic forces to the side of the electrode having a polarityopposite to that of charges of the migratory particles themselves basedon the electrophoresis of charged particles. Display of information isperformed by coloring the migratory particles and utilizing a differencebetween the color of the migratory particles and the color of the dyeddielectric liquid. More specifically, when the migratory particles areattracted onto the surface of a first electrode that is closer to theviewer and is light transparent, the color of the migratory particles isobserved. On the contrary, when the migratory particles are attractedonto the surface of a second electrode that is farther away from theviewer, the color of the dielectric liquid, which is dyed so as to havedifferent optical characteristics from those of the migratory particles,is observed.

In the above-described electrophoretic display device, however, a dyeand a coloring material in the form of ions, for example, must be mixedin the dielectric liquid, and the presence of such a coloring materialtends to act as an unstable factor in the electrophoretic operationbecause of giving rise to a new transfer of charges. This tendency maydeteriorate the performance, useful life and stability of the displaydevice.

To overcome the above problem, Japanese Patent Laid-Open Nos. 49-5598and 11-202804 propose a display device wherein a pair of electrodes,i.e., first and second driving electrodes, are arranged on the samesubstrate and migratory particles are migrated horizontally as viewedfrom the viewer. By applying voltages to the first and second drivingelectrodes, the migratory particles in a transparent dielectric liquidare horizontally migrated parallel to the substrate surface between thefirst and second driving electrodes based on the electrophoresis ofcharged particles, whereby an image is displayed.

In such an electrophoretic display device of the horizontally migratingtype, the dielectric liquid is transparent and the first and seconddriving electrodes have different colors as viewed from the viewer sidesuch that the color of one electrode coincides with the color of themigratory particles. Assuming, for example, that the color of the firstdriving electrode is black, the color of the second driving electrode iswhite, and the color of the migratory particles is black. The seconddriving electrode is exposed to provide a white view when the migratoryparticles are distributed over the first driving electrode, and theblack color of the migratory particles is viewed when the migratoryparticles are distributed over the second driving electrode.

A display device comprising a large number of pixels arranged in amatrix pattern is electrically addressed in two primary ways, i.e., anactive matrix mode and a passive matrix mode.

In the active matrix mode, a switching element such as a thin filmtransistor (TFT) is formed corresponding to each pixel, and voltagesapplied to the pixels are controlled in an independent manner for eachpixel. By using the active matrix mode, the electrophoretic displaydevice of the horizontally migrating type can be operated with a highdisplay contrast. However, the active matrix mode has problems that theprocess cost is relatively high and it is difficult to form thin filmtransistors on a polymer substrate because of a high process temperaturerequired in formation of the thin film transistors. These problems areparticularly critical to manufacture of a paper-like display that isintended to be low in cost and flexible. A process for forming thin filmtransistors with a polymer material, which is adaptable for printing, isproposed to overcome those problems, but it is still an unknown quantityin practical applicability.

In the passive matrix mode, since only X-Y electrode lines are requiredas components necessary for addressing, the cost is relatively low andthe electrodes lines can be easily formed on a polymer substrate. Whenapplying a write voltage to a selected pixel, a voltage corresponding tothe write voltage is applied to the X- and Y-electrode lines that crosseach other at a point defining the selected pixel. In general, however,where an electrophoretic display device is operated by the passivematrix mode, there occurs so-called crosstalk, i.e., a phenomenon thatthe write voltage is applied to not only the selected pixel but alsoother pixels around it, whereby the display contrast is noticeablydeteriorated. This is a problem that takes place inevitably because theelectrophoretic display device does not have a definite thresholdcharacteristic with respect to the write voltage.

To cope with the above-mentioned problem, it has been proposed torealize the passive matrix addressing in an electrophoretic displaydevice, which does not have a threshold in principle, by employing athree-electrode structure wherein a control electrode is provided inaddition to a pair of display electrodes. Most proposals regarding thethree-electrode structure are related to electrophoretic display devicesof the type using vertically arranged electrodes, as disclosed in, byway of example, Japanese Patent Laid-Open No. 54-085699 (correspondingto U.S. Pat. No. 4,203,106).

For a three-electrode structure in the electrophoretic display device ofthe horizontally migrating type, only one proposal is disclosed inJapanese Patent Publication No. (by PCT application) 8-507154(corresponding to U.S. Pat. No. 5,345,251). However, a disperse solutionused in Japanese Patent Publication No. (by PCT application) 8-507154seems to be not transparent, but colored. This related art thereforediffers in category from the electrophoretic display devices of thehorizontally migrating type, which are featured by using a transparentdisperse solution, as disclosed in the above-cited Japanese PatentLaid-Open Nos. 49-5598 and 11-202804 and as intended by the presentinvention.

Japanese Patent Publication No. (by PCT application) 8-507154 disclosestwo types of constructions (FIGS. 17A and 17B of the attached drawings).In the first construction (FIG. 17A), a control electrode 14 is arrangedas a third electrode on the side of a second substrate 2 in anelectrophoretic display device of the horizontally migrating type. Inthe second construction (FIG. 17B), a control electrode 14 is arrangedas a third electrode between a first driving electrode 3 and a seconddriving electrode 4 both arranged on the side of a first substrate 1.

In any type of the first and second constructions, the first drivingelectrode 3 in the forked form as an assembly of a plurality of lineelectrodes and the second driving electrode 4 in the forked form as anassembly of a plurality of line electrodes, which are laid betweenadjacent lines of the first driving electrode 3, are both arranged onthe first substrate 1 within an area of each pixel. The second drivingelectrode 4 is arranged on a step 15 formed by a thick chrome film.Accordingly, a level difference 22 of about 0.3 μm is formed at theboundary between the first driving electrode 3 and the second drivingelectrode 4. In the first construction, the control electrode 14 isformed on the underside of the second substrate 2 over the entiresurface of each pixel area, the second substrate 2 being arranged in anopposing relation to the first substrate 1 with a spacing of 25 μm to116 μm left between both the electrodes. In the second construction, thecontrol electrode 14 is arranged on the first substrate 1 betweenrespective lines of the first driving electrode 3 and the second drivingelectrode 4. In FIGS. 17A and 17B, for the sake of explanation, thefirst driving electrode 3 and the second driving electrode 4 are eachillustrated as being constituted by one line.

The write operation of the electrophoretic display device disclosed inJapanese Patent Publication No. (by PCT application) 8-507154 will bedescribed with reference to FIGS. 18 and 19. FIG. 18 shows migratoryparticles in respective operational conditions, and FIG. 19 showsapplied pulses and a change of reflectance. The cell construction is thesame as that shown in FIG. 17A (except for only one pixel being shown inFIG. 18).

Note that values of applied voltages mentioned in the followingdescription are ones obtained under conditions of an experiment actuallyconducted by the inventors, and the conditions of the experiment are notexactly coincident with those described in Japanese Patent PublicationNo. (by PCT application) 8-507154. Such a discrepancy in thoseconditions primarily depends on differences in physical properties suchas the polarity and amount of charges on migratory particles used.Hereunder, the values of applied voltages, which were obtained asresults of the experiment made on the migratory particles used by theinventors, are employed for easier comparison with the operation of thepresent invention described later.

Also, although it seems that a colored liquid is used as a dielectricsolution in Japanese Patent Publication No. (by PCT application)8-507154, a transparent dielectric liquid is used in the followingdescription for easier comparison with the operation of the presentinvention described later. Furthermore, for a method of developingdisplay contrast, the following description is made as using a similarmethod to that employed in embodiments of the present invention whereinthe color of the migratory particles is black, the color of the firstdriving electrode is black, and the color of the second drivingelectrode is white.

It is supposed that the migratory particles 6 are positively charged,the first driving electrode 3 serves as a common electrode, and adriving voltage Vd and a control voltage Vc are applied respectively tothe first driving electrode 3 and the control electrode 14 with theground potential of the second driving electrode 4 being as a reference.

In FIG. 8, a time period Ta represents a state where a white view ismaintained. Also, arrows schematically indicate vectors of an electricfield produced in a cell. The migratory particles 6 collected over thefirst driving electrode 3 are restrained from moving toward the side ofthe second driving electrode 4 due to the presence of the leveldifference 22 between the first driving electrode 3 and the seconddriving electrode 4. At the same time, the migratory particles 6 areheld down to be urged toward the first substrate side under the controlvoltage Vc=+250 V applied between the first driving electrode 3 and thecontrol electrode 14. During this time period Ta, therefore, themigratory particles 6 are stabilized in a condition as shown and a whiteview state with a reflectance R of about 70% is maintained. The drivingvoltage Vd=+5 V applied to the first driving electrode 3 in a state, inwhich a current view is maintained, serves to suppress a tendency of themigratory particles 6 near the level difference 22 to migrate toward theside of the first driving electrode 3 in the black view maintainedstate.

In a write period Tb, the driving voltage Vd=+50 V and the controlvoltage Vc=+50 V are applied. Since the first driving electrode 3 andthe control electrode 14 are set to the same potential, the migratoryparticles 6 are released from being held down under the control voltage,whereby all of the migratory particles 6 are horizontally migratedtoward the side of the second driving electrode 4 along the drivingelectrode surfaces beyond the level difference 22. As a result, thereflectance R abruptly decreases.

In a time period Tc representing a state in which a black view ismaintained, the migratory particles 6 are held down to be urged towardthe first substrate side as shown under the control voltage Vc=+250 V.Accordingly, a black view state with a reflectance R of about 5% ismaintained.

The passive matrix addressing method disclosed in Japanese PatentPublication No. (by PCT application) 8-507154 will be described belowwith reference to FIGS. 20 and 21. Let us assume an electrophoreticdisplay device of the horizontally migrating type has an (m×n) matrixwherein m columns of pixels are arrayed in the X-direction and n rows ofpixels are arrayed in the Y-direction. Corresponding to the arrayconfiguration of pixels, a number m of data-signal electrode linesconnected to the control electrodes 14 are arranged in the columndirection, and a number n of scan-signal electrode lines connected tothe first driving electrodes 3 are arranged in the row direction, withboth the lines crossing each other in an orthogonal relation. The seconddriving electrode 4 is fixedly maintained at the ground potential so asto serve as a common electrode.

First, Vd=−50 V is applied to all of the scan-signal electrode lines andVc=0 V is applied to all of the data-signal electrode lines so that allof the migratory particles 6 are collected over the first drivingelectrode 3 (FIG. 20A, total erasure). Then, the scan-signal electrodelines are selected one by one in sequence from the top in theY-direction for writing. In a selection period (write period), Vd=+50 Vis applied to the scan-signal electrode lines, Vc=+50 V is applied tothose ones of the data-signal electrode lines corresponding to selectedpixels, and Vc=+250 V is applied to the other ones of the data-signalelectrode lines corresponding to non-selected pixels. For the selectedpixels, the migratory particles 6 are migrated to the side of the seconddriving electrode 4 beyond the level difference under the drivingvoltage Vd=+50 V applied between the first and second driving electrode3, 4, whereby writing is performed (FIG. 20B). For the non-selectedpixels, the driving voltage Vd=+50 V is also applied to the firstdriving electrode 3. In the first construction, however, the migratoryparticles 6 are held down to be urged onto the first driving electrode 3under the control voltage Vc=+250 V and are prevented from migrating (toperform writing) (FIG. 20C).

On the other hand, in a non-selection period, Vd=+5 V is applied to thescan-signal electrode lines, and Vc=+50 V or +250 V is applied to thedata-signal electrode lines (FIGS. 21A to 21D). In any case, themigratory particles 6 are held down to be urged onto the surface of thefirst substrate as shown under the control voltage.

Thus, writing of information is performed by the passive matrixaddressing method in the electrophoretic display device of thehorizontally migrating type that does not have a thresholdcharacteristic.

However, the following problems are experienced with the electrophoreticdisplay device of the horizontally migrating type disclosed in JapanesePatent Publication No. (by PCT application) 8-507154.

The disclosed first construction has a limitation that the leveldifference 22 defined by the step 15 cannot be set to a large value. Ifthe level difference is too large, part of the charged migratoryparticles 6 could not move over the level difference and would remain onthe lower one of two surfaces defining the level difference when forcedto migrate in the selection period, thus resulting in a reduced displaycontrast (FIG. 22A). To avoid the migratory particles 6 from remainingon the lower surface, the height of the step 15 must be limited to avalue approximately equal to the diameter of the migratory particles 6.

Due to such a limitation imposed on the height of the step 15, the leveldifference cannot provide the effect of suppressing the migration of themigratory particles 6 at a sufficient level. Accordingly, when applyingthe control voltage Vc to hold down the migration of the migratoryparticles 6 for the non-selected pixel (FIG. 20C) in a condition wherethe driving voltage Vd is applied in the selection period, part of themigratory particles 6 moves over the level difference because of thestep 15 being low. This phenomenon gives rise to a serious problem thatcrosstalk occurs and the display contrast deteriorates (FIG. 22B).

If the control voltage Vc is set to a sufficiently high value, theundesired migration of the migratory particles 6 can be prevented to anearly satisfactory extent. However, this solution not only has thedisadvantage of increasing the applied voltage, but also brings aboutanother problem that charges injected into dielectric components of thedevice under a high voltage remain there even after release of the highvoltage, and the operational condition of the migratory particles 6becomes unstable due to an unintended electric field caused by theremaining charges.

The limitation imposed on the height of the step 15 raises still anotherproblem as follows. Since the height of the step 15 is not sufficient,the area difference between the first driving electrode 3 and the seconddriving electrode 4 cannot be set to a large value. If the areadifference is set to a large value, the migratory particles 6 would flowover onto the electrode surface having a larger area even when themigratory particles 6 are urged such that they are all collected on theelectrode surface having a smaller area (FIG. 22C). Consequently, thedisplay contrast is restricted because it is determined by an area ratiobetween the first driving electrode 3 and the second driving electrode4.

Further, in the disclosed first construction (FIG. 17A), the effect ofsuppressing the migration of the migratory particles 6, provided by thelevel difference, is restricted only in the direction toward the highersurface side from the lower surface side, whereas the migration of themigratory particles 6 from the higher surface side to the lower surfaceside is rather accelerated. The write direction is therefore limited toonly one direction from a white to black view. In other words, theaddressing method for writing is restricted to the steps of firstcollecting the migratory particles 6 for an overall screen to the lowersurface side for total reset, and then writing information by migratingthe migratory particles 6 in one direction to the higher surface side.It is hence impossible to perform bi-directional writing, i.e.,black-to-white and white-to-black writing, and to realize such anoperation as selectively rewriting only part of an image on the screen.

The disclosed second construction (FIG. 17B) operates in the selectionperiod such that a high voltage is applied to the control electrode 14for the non-selected pixel to prevent the migratory particles 6 frommoving in both directions, and the voltage of the control electrode 14is set to 0 V for the selected pixel, allowing the migratory particles 6to smoothly migrate in either direction. In this case, therefore, thestep 15 is considered to not be an essential component.

In the disclosed second construction, however, the control electrode 14is able to control the migration of the migratory particles 6 onlybetween the first and second driving electrodes, and is unable tocontrol the migration of the migratory particles 6 within each of thedriving electrode surfaces. Due to a control voltage applied to thecontrol electrode 14 in the non-selection period, therefore, themigratory particles 6 having been evenly dispersed over the drivingelectrode surface are repellently migrated in a direction away from thecontrol electrode 14 and are partially distributed within the drivingelectrode surface as shown in FIG. 23A or 23B. This invites a problem ofnoticeably reducing the display contrast.

SUMMARY OF THE INVENTION

With the view of overcoming the problems set forth above, it is anobject of the present invention to provide a novel electrophoreticdisplay method and device, which have the following features.

According to one aspect of the present invention, in an electrophoreticdisplay method for use in an electrophoretic display device comprising afirst substrate, first and second driving electrodes arranged on thefirst substrate, a second substrate arranged in an opposing relation tothe first substrate, a third driving electrode arranged on the secondsubstrate, a transparent dielectric liquid filled between the firstsubstrate and the second substrate, and a plurality of migratoryparticles dispersed in the transparent dielectric liquid. The methodcomprises, for display of information, a first step of migrating themigratory particles between the first driving electrode and the seconddriving electrode; and a second step of migrating the migratoryparticles between the first driving electrode or the second drivingelectrode and the third driving electrode.

Preferably, the electrophoretic display method further comprises a stepof applying voltages to the first driving electrode, the second drivingelectrode and the third driving electrode to provide a time period inwhich a relationship of potentials of the first driving electrode andthe second driving electrode being higher than a potential of the thirddriving electrode is satisfied for positively charged migratoryparticles, or a time period in which a relationship of potentials of thefirst driving electrode and the second driving electrode being lowerthan a potential of the third driving electrode is satisfied fornegatively charged migratory particles. The migratory particles areattracted onto the third driving electrode arranged on the secondsubstrate.

Preferably, the electrophoretic display method further comprises a stepof rewriting display through a first stage of moving the migratoryparticles, which are attracted onto the third driving electrode, awayfrom the third driving electrode, a second stage of migrating themigratory particles between the first driving electrode and the seconddriving electrode, and a third stage of attracting the migratoryparticles onto the third driving electrode.

Preferably, the electrophoretic display method further comprises a stepof applying voltages to the first driving electrode, the second drivingelectrode and the third driving electrode to provide a time period inwhich a relationship of potentials of the first driving electrode andthe second driving electrode being lower than a potential of the thirddriving electrode is satisfied for positively charged migratoryparticles, or a time period in which a relationship of potentials of thefirst driving electrode and the second driving electrode being higherthan a potential of the third driving electrode is satisfied fornegatively charged migratory particles. The migratory particles aremoved away from the third driving electrode arranged on the secondsubstrate.

As an alternative, preferably, the electrophoretic display methodfurther comprises a step of rewriting display through a first stage ofmoving the migratory particles, which are attracted onto the thirddriving electrode, away from the third driving electrode, andsimultaneously migrating the migratory particles onto the first drivingelectrode or the second driving electrode, and a second stage ofattracting the migratory particles to the second substrate side.

According to another aspect of the present invention, an electrophoreticdisplay device comprises a first substrate; first and second drivingelectrodes arranged on the first substrate; a second substrate arrangedin an opposing relation to the first substrate; a third drivingelectrode arranged on the second substrate; and a transparent dielectricliquid filled between the first substrate and the second substrate. Aplurality of migratory particles are dispersed in the transparentdielectric liquid, and a barrier is disposed on a surface of the thirddriving electrode arranged on the second substrate, with the barrierbeing situated in an opposing relation to a boundary between the firstdriving electrode and the second driving electrode.

According to still another aspect of the present invention, anelectrophoretic display device comprises a first substrate; first andsecond driving electrodes arranged on the first substrate; a secondsubstrate arranged in an opposing relation to the first substrate; athird driving electrode arranged on the second substrate; and atransparent dielectric liquid filled between the first substrate and thesecond substrate. A plurality of migratory particles are dispersed inthe transparent dielectric liquid, and a charged film disposed on asurface of the third driving electrode is arranged on the secondsubstrate, with the charged film having surface charges which areconstantly electrified with a polarity opposite to that of the chargedmigratory particles.

Preferably, the electrophoretic display device further comprisesinsulating layers arranged to cover the first driving electrode, thesecond driving electrode, and the third driving electrode.

Preferably, at least one of the first driving electrode, the seconddriving electrode, the third driving electrode, the first substrate, thesecond substrate, and the insulating layers is colored in a color havingdifferent optical characteristics from those of the migratory particles.

Preferably, the first substrate and the second substrate are each formedof a polymer film.

Preferably, an average diameter of the migratory particles is in therange of 0.1 μm to 10 μm.

Preferably, the distance between the first substrate and the secondsubstrate is not larger than 500 μm.

Preferably, the distance between the first substrate and the secondsubstrate is not larger than 100 μm.

Preferably, the distance between the first substrate and the secondsubstrate is not smaller than the diameter of the migratory particles.

Preferably, the distance between the first substrate and the secondsubstrate is not smaller than twice the diameter of the migratoryparticles.

Preferably, the distance between the first substrate and the secondsubstrate is not smaller than five times the diameter of the migratoryparticles.

Preferably, the first substrate and the migratory particles are black ordeep black in color.

With the electrophoretic display method and device set forth above, thevoltage required to inhibit the migration of the migratory particles andhold them at a standstill can be reduced to a large extent in comparisonwith that required in a conventional electrophoretic display devicedisclosed in the above-cited Japanese Patent Publication No. (by PCTapplication) 8-507154, for example, when operated with a conventionalpassive matrix addressing method.

The present invention proposes a novel passive matrix addressing methodbased on a transfer display technique in which a pseudo threshold isprovided by transferring a display pattern onto the third drivingelectrode arranged on the second substrate. In other words, the passivematrix addressing method of the present invention differs basically fromthe conventional passive matrix addressing method in which a controlelectrode is employed to apply a high control voltage for holding downthe migratory particles and inhibiting the migration of them, asdisclosed in the above-cited Japanese Patent Publication No. (by PCTapplication) 8-507154.

More specifically, in accordance with the novel method of the presentinvention, the passive matrix addressing method can be realized bymigrating the migratory particles between the first driving electrodeand the second driving electrode to form a display pattern, and thenattracting the migratory particles onto the third driving electrodearranged on the second substrate, whereby the display pattern istransferred onto the second substrate side.

The reason why the novel passive matrix addressing method can berealized is based on two phenomena. First, since the migratory particlesare drawn under a driving voltage applied to the third driving electrodeand are attracted onto the third driving electrode, the migratoryparticles become hard to horizontally migrate under electric fieldsproduced by voltages applied to the first and second driving electrodes.Secondly, on the side of the second substrate that is disposed in anopposing relation to the first and second driving electrodes with acertain distance left between them, the electric fields produced by thevoltages applied to the first and second driving electrodes areweakened. Therefore, even when the voltages applied to the first andsecond driving electrodes are changed, the migratory particles avoidbeing affected by resulting changes of the electric fields.

Because the above two phenomena act effectively on the migratoryparticles, a high voltage is not required to be applied to the thirddriving electrode. Further, in a state where the display pattern istransferred onto the third driving electrode, even when the voltagesapplied to the first and second driving electrodes are changed, themigratory particles maintain the previous condition and the displaypattern formed before the voltage changes remains the same.Consequently, the present invention has a very valuable advantage that,in spite of the migratory particles not having a definite thresholdcharacteristic with respect to the driving voltage, it is possible toinhibit the migration of the migratory particles and hold them at astandstill even under a relatively low voltage, whereby anelectrophoretic display device can be operated with a passive matrixaddressing method in a satisfactory manner.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of one typical example of a display device ofthe present invention;

FIGS. 2A and 2B are each a plan view of one typical example of thedisplay device of the present invention;

FIGS. 3A and 3B are each a sectional view of another typical example ofthe display device of the present invention;

FIGS. 4A, 4B and 4C are explanatory views showing part of an addressingmethod and operational conditions in the display device of the presentinvention;

FIGS. 5A, 5B and 5C are explanatory views showing other parts of theaddressing method and operational conditions in the display device shownin FIG. 4;

FIGS. 6A to 6H are explanatory views showing part of one passive matrixaddressing method for the display device of the present invention;

FIGS. 7A to 7F are explanatory views showing other parts of the onepassive matrix addressing method for the display device shown in FIG. 6;

FIGS. 8A to 8F are explanatory views showing part of another passivematrix addressing method for the display device of the presentinvention;

FIGS. 9A to 9D are explanatory views showing other parts of anotherpassive matrix addressing method for the display device shown in FIG. 8;

FIG. 10 is a sectional view of still another typical example of thedisplay device of the present invention;

FIG. 11 is a sectional view of still another typical example of thedisplay device of the present invention;

FIG. 12 is a sectional view of still another typical example of thedisplay device of the present invention;

FIGS. 13A and 13B are each a sectional view of still another typicalexample of the display device of the present invention;

FIG. 14 is a plan view showing a configuration of a 3×3 matrixfabricated in Example 1 of the present invention;

FIGS. 15A and 15B show respectively a time chart and a display patternfor matrix addressing performed in Example 1 of the present invention;

FIGS. 16A and 16B show respectively a time chart and a display patternfor matrix addressing performed in Example 2 of the present invention;

FIGS. 17A and 17B are each a sectional view of a conventional displaydevice;

FIG. 18 shows an addressing method and operational conditions in oneconventional display device;

FIG. 19 is a chart showing the addressing method and operationalconditions in the one conventional display device;

FIGS. 20A, 20B and 20C are explanatory views showing part of a passivematrix addressing method in the one conventional display device;

FIGS. 21A to 21D are explanatory views showing other parts of thepassive matrix addressing method in the one conventional display device;

FIGS. 22A, 22B and 22C are schematic views for explaining problems withthe one conventional display device;

FIGS. 23A and 22B are schematic views for explaining a problem with theother conventional display device;

FIG. 24 is a plan view showing a configuration of a 3×3 matrixfabricated as a Comparative Example; and

FIGS. 25A and 25B show respectively a time chart and a display patternfor matrix addressing performed in the Comparative Example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments will be described below with reference to thedrawings.

(Basic Construction and Operation)

FIG. 1 is a sectional view showing one typical example of a constructionof a display device of the present invention. For the sake ofexplanation, FIG. 1 illustrates the construction comprising two pixels.A first substrate 1 and a second substrate 2 are arranged in an opposingrelation with partitions 10 provided between both substrates. A firstdriving electrode 3 and a second driving electrode 4 are formed on anupper surface of the first substrate 1, whereas a third drivingelectrode 5 is formed on a lower surface of the second substrate 2. Atransparent dielectric liquid 7 is filled in the space defined by boththe substrates 1, 2 and the partitions 10, and charged migratoryparticles 6 are dispersed in the dielectric liquid 7.

Plan shapes of the first driving electrode 3 and the second drivingelectrode 4 are not limited to particular ones. One typical example is astriped electrode (shown in FIG. 2A). In addition, each electrode mayhave any suitable shape such as being rectangular (FIG. 2B) or in theform of a circular or other closed loop.

Practical sizes of the construction shown in FIG. 1 are preferably set,by way of example, such that for a pixel size of 100 μm×100 μm, theaverage diameter of the migratory particles 6 is 1 μm, the spacingbetween the first and second substrates 1, 2 is 80 μm, and an area ratiowith respect to the total pixel area is 15% for the first drivingelectrode 3 and 85% for the second driving electrode 4.

Cell components of the display device can be colored in any desiredcombination. For example, the color of the migratory particles 6 isblack, the second substrate 2 is transparent, the color of the firstdriving electrode 3 is black, the color of the second driving electrode4 is white, and the third driving electrode 5 is transparent. Thiscombination provides monochrome display in which a white view and ablack view can be selectively switched over when the viewer looks at thecell from the second substrate side. Color display is also possible bycoloring and arranging the second driving electrodes 4 so as to providered, green and blue pixels, or by forming the second driving electrode 4to be transparent and coloring the first substrate 1 so as to providered, green and blue pixels, or forming the second driving electrode 4 tobe transparent and providing an insulating layer 11 colored so as toprovide red, green and blue pixels on the first substrate 1, as shown inFIG. 3A.

The viewer is not always required to look at the cell from the secondsubstrate side. When the viewer looks at the cell from the firstsubstrate side, a white view and a black view can be selectivelyswitched over to provide monochrome display by employing a combinationthat the color of the migratory particles 6 is black, the firstsubstrate 1 is transparent, the color of the first driving electrode 3is black, the second driving electrode 4 is transparent, and the colorof the third driving electrode 5 is white. Also, in this case, colordisplay is possible by coloring and arranging the third drivingelectrodes 5 so as to provide red, green and blue pixels, or by formingthe third driving electrode 5 to be transparent and coloring the secondsubstrate 2 so as to provide red, green and blue pixels, or forming thesecond driving electrode 4 to be transparent and providing an insulatinglayer 11 colored so as to provide red, green and blue pixels on theunderside of the second substrate 2, as shown in FIG. 3B.

Significant features of the addressing method used in the presentinvention will now be described with reference to FIGS. 4 and 5. FIGS. 4and 5 show operational conditions of the migratory particles insuccessive steps of the addressing method. The following description ismade on the premise that the migratory particles 6 are positivelycharged, and the components are colored such that the migratoryparticles 6 are black, the first driving electrode 3 is black, thesecond driving electrode 4 is white, and the third driving electrode 5is transparent. Arrows in FIGS. 4 and 5 schematically indicate vectorsof an electric field produced in the cell. The cell construction is thesame as that shown in FIG. 1. Further, it is assumed that a drivingvoltage Vd1 is applied to the first driving electrode 3, a drivingvoltage Vd2 is applied to the second driving electrode 4, and a drivingvoltage Vd3 is applied to the third driving electrode 5. Additionally,it is to be noted that voltage values indicated in the followingdescription do not represent ones which must be always employed inpractice, and can be set as desired so long as the display method of thepresent invention is realized.

First, the driving voltages are applied to the first driving electrode 3and the second driving electrode 4 so that the migratory particles 6 arehorizontally migrated (FIG. 4A). More specifically, for a pixel A, thedriving voltage Vd1=−30 V is applied to the first driving electrode 3and the driving voltage Vd2=+30 V is applied to the second drivingelectrode 4, thereby providing a white view state. For a pixel B, thedriving voltage Vd1=+30 V is applied to the first driving electrode 3and the driving voltage Vd2=−30 V is applied to the second drivingelectrode 4, thereby providing a black view state. At this time, thedriving voltage Vd3=+60 V is applied to the third driving electrode 5.

Subsequently, the driving voltage Vd3=−60 V is applied to the thirddriving electrode 5, causing the migratory particles 6 to be attractedonto the third driving electrode 5 by electrostatic forces. At thistime, as shown in FIG. 4B, the migratory particles 6 in pixel A aretransferred onto an area of the second substrate surface positioned inan opposing relation to the first driving electrode 3, and the migratoryparticles 6 in pixel B are transferred onto an area of the secondsubstrate surface positioned in an opposing relation to the seconddriving electrode 4. Therefore, the pixel A is held in the white viewstate and the pixel B is held in the black view state.

In the above condition, the polarity of the driving voltage applied toeach of the first and second driving electrodes is reverted. Morespecifically, for the pixel A, the driving voltage Vd1=+30 V is appliedto the first driving electrode 3 and the driving voltage Vd2−−30 V isapplied to the second driving electrode 4. For the pixel B, the drivingvoltage Vd1=−30 V is applied to the first driving electrode 3 and thedriving voltage Vd2=+30 V is applied to the second driving electrode 4.In spite of such a reversal of the polarity, the display state is notchanged (FIG. 4C).

Electric fields produced by the voltage applied to the first drivingelectrode 3 and the voltage applied to the second driving electrode 4are strong on the first substrate side and are gradually weakened as apoint comes closer to the second substrate 2 away from the firstsubstrate 1. Thus, the migratory particles 6 are substantially perfectlyprevented from migrating horizontally because of two phenomena; i.e.,the migratory particles 6 are attracted onto the third driving electrode5 under the driving voltage applied to the third driving electrode 5,and the electric field tending to horizontally migrate the migratoryparticles 6 is weak on the second substrate side. As compared with theconstruction disclosed in Japanese Patent Publication No. (by PCTapplication) 8-507154, therefore, the voltage required to inhibit themigration of the migratory particles 6 and hold them at a standstill canbe reduced to a large extent. This feature is the most importantadvantage of the present invention. In other words, the above feature isvery effective in driving an electrophoretic display device, which doesnot have a definite threshold characteristic with respect to the drivingvoltage, by the passive matrix addressing method.

The present invention proposes two types of addressing methods forrewriting of a displayed image.

[Rewriting Method 1]

According to one display rewriting method, as shown in FIG. 5A, thedriving voltages Vd1=Vd2=0 V are applied to the first and second drivingelectrodes 3, 4, and the driving voltage Vd3=+60 V is applied to thethird driving electrode 5, whereby the migratory particles 6 aremigrated away from the second substrate 2 toward the first substrateside. Then, desired display is performed pixel by pixel. Assuming thatthe pixel A should provide a black view, the driving voltage Vd1=+30 Vis applied to the first driving electrode 3 and the driving voltageVd2=−30 V is applied to the second driving electrode 4. Also, assumingthat the pixel B should provide a white view, the driving voltage Vd1=−30 V is applied to the first driving electrode 3 and the drivingvoltage Vd2=+30 V is applied to the second driving electrode 4. Themigratory particles 6 are thereby migrated as desired (FIG. 5B).Subsequently, Vd3=−60 V is applied to the third driving electrode 5again for transferring the migratory particles i.e., the displaypattern, to the second substrate side as shown in FIG. 4B.

[Rewriting Method 2]

The other display rewriting method will now be described. According tothis method, at the same time as applying the driving voltage Vd3=+60 Vto the third driving electrode 5 to migrate the migratory particles 6away from the second substrate 2 toward the first substrate side, thedriving voltages are applied to the first driving electrode 3 and thesecond driving electrode 4 for writing.

More specifically, as shown in FIG. 5C, at the moment when the drivingvoltage Vd3=+60 V is applied to the third driving electrode 5, thedriving voltage Vd1=+30 V is applied to the first driving electrode 3and the driving voltage Vd2=−30 V is applied to the second drivingelectrode 4 for the pixel A that should provide a black view, while thedriving voltage Vd1=−30 V is applied to the first driving electrode 3and the driving voltage Vd2=+30 V is applied to the second drivingelectrode 4 for the pixel B that should provide a white view. Themigratory particles 6 are thereby migrated onto the first drivingelectrode 3 or the second driving electrode 4 to form a display pattern.Subsequently, Vd3=−60 V is applied to the third driving electrode 5again for transferring the migratory particles, i.e., the displaypattern, to the second substrate side as shown in FIG. 4B. This methodis advantageous in shortening a write time.

(Passive Matrix Addressing Methods)

Two types of passive matrix addressing methods used in the presentinvention will be described below with reference to FIGS. 6 to 9. Arrowsin FIGS. 6 and 9 schematically indicate vectors of an electric fieldproduced in the cell. Let assume an electrophoretic display device ofthe horizontally migrating type that has an (m×n) matrix wherein mcolumns of pixels are arrayed in the X-direction and n rows of pixelsare arrayed in the Y-direction. Corresponding to the array configurationof pixels, a number m of first data-signal electrode lines connected tothe first driving electrodes 3 and a number m of second data-signalelectrode lines connected to the second driving electrode 4 are arrangedin the column direction, and a number n of scan-signal electrode linesconnected to the third driving electrodes 5 are arranged in the rowdirection, the two kinds of lines crossing each other in an orthogonalrelation.

[Passive Matrix Addressing Method 1]

Writing is performed in accordance with the above-described RewritingMethod 1 by selecting the scan-signal electrode lines one by one insequence from the top in the Y-direction. The operation carried out forthe selected scan-signal electrode line, which is also simply called theselected line, is first described. It is assumed that, in the displaycondition prior to the start of writing, a pixel to be rewritten toprovide a white view is providing a black view (FIG. 6A), a pixel to berewritten to provide a black view is providing a white view (FIG. 6B),and these black and white views are reversed upon writing.

In the selected line, as shown in FIGS. 6C and 6D, the driving voltageVd3=+60 V is applied to the scan-signal electrode line, and at the sametime the driving voltages Vd1=Vd2=0 V are applied to the first andsecond data-signal electrode lines, whereby the migratory particles 6are migrated away from the third driving electrode 5 toward the firstsubstrate side. Then, for each of those pixels in the selected linewhich should provide a white view, Vd1=30 V is applied to the firstdata-signal electrode line and Vd2=+30 V is applied to the seconddata-signal electrode line (FIG. 6E). Also, for each of those pixels inthe selected line which should provide a black view, Vd1=+30 V isapplied to the first data-signal electrode line and Vd2=−30 V is appliedto the second data-signal electrode line (FIG. 6F). With suchapplication of the driving voltages, the migratory particles 6 arehorizontally migrated onto the first driving electrode 3 or the seconddriving electrode 4, thereby providing desired display.

After completion of the horizontal migration of the migratory particles6, Vd3=−60 V is applied to the relevant scan-signal electrode line,whereupon the migratory particles 6 are attracted onto the third drivingelectrode 5 so that the display pattern is transferred to the secondsubstrate side (FIGS. 6G and 6H). The operation to be carried out forthe selected line is thus ended, and the similar write operation is thenrepeated for a next line as the selected line.

In the non-selected line, as shown in FIGS. 7A to 7F, the drivingvoltage Vd3=−60 V is continuously applied to the scan-signal electrodeline. To the first and second data-signal electrode lines, there areapplied −30 V or +30 V that is used when providing a white or blackview, and then 0 V that is used when migrating the migratory particles 6toward the first substrate side. However, since the migratory particles6 are still attracted onto the second substrate side under the drivingvoltage applied to the third driving electrode 5, they will nothorizontally migrate in spite of the driving voltages applied to thefirst and second data-signal electrode lines being changed between +30V, 0 V and −30 V. As a result, the previous display condition can beheld with stability.

[Passive Matrix Addressing Method 2]

Writing is performed in accordance with the above-described RewritingMethod 2 by selecting the scan-signal electrode lines one by one insequence from the top in the Y-direction. The operation carried out forthe selected scan-signal electrode line, which is also simply called theselected line, is first described. As with the above description ofPassive Matrix Addressing Method 1, it is assumed that, in the displaycondition prior to the start of writing, a pixel to be rewritten toprovide a white view is providing a black view (FIG. 8A), a pixel to berewritten to provide a black view is providing a white view (FIG. 8B),and these black and white views are reversed upon writing.

In the selected line, the driving voltage Vd3=+60 V is applied to thescan-signal electrode line for migrating the migratory particles 6toward the first substrate side. At the same time as applying thedriving voltage Vd3=+60 V, the respective driving voltages required forproviding desired display are applied to the first and seconddata-signal electrode lines, whereby the migratory particles 6 aremigrated onto the first driving electrode 3 or the second drivingelectrode 4. More specifically, for each of those pixels in the selectedline which should provide a white view, Vd1=−30 V is applied to thefirst data-signal electrode line and Vd2=+30 V is applied to the seconddata-signal electrode line (FIG. 8C). Also, for each of those pixels inthe selected line which should provide a black view, Vd1=+30 V isapplied to the first data-signal electrode line and Vd2=−30 V is appliedto the second data-signal electrode line (FIG. 8D). After completion ofthe migration of the migratory particles 6, Vd3=−60 V is applied to therelevant scan-signal electrode line, whereupon the migratory particles 6are attracted onto the third driving electrode 5 so that the displaypattern is transferred to the second substrate side (FIGS. 8E and 8F).

In the non-selected line, as shown in FIGS. 9A to 9D, the drivingvoltage Vd3=−60 V is continuously applied to the scan-signal electrodeline. To the first and second data-signal electrode lines, there areapplied −30 V or +30 V that is used when providing a white or blackview, and then 0 V that is used when migrating the migratory particles 6toward the first substrate side. However, since the migratory particles6 are still attracted onto the second substrate side under the drivingvoltage applied to the third driving electrode 5, they will nothorizontally migrate in spite of the driving voltages applied to thefirst and second data-signal electrode lines being changed between +30 Vand −30 V. As a result, the previous display condition can be held withstability.

Thus, in the electrophoretic display device of the horizontallymigrating type according to the present invention, a high quality imagecan be displayed by the passive matrix addressing without causing anycrosstalk.

(Variations of Construction)

The addressing method as the feature of the present invention is notlimited in its applications to the display device having theconstruction shown in FIG. 1. Other constructions of the display device,to which the addressing method of the present invention is effectivelyapplicable, will be described below with reference to the drawings.

FIG. 10 shows a construction of the display device of the presentinvention wherein a barrier 12 is provided as an obstacle on the surfaceof the third driving electrode 5 arranged on the underside of the secondsubstrate 2. More specifically, the barrier 12 is provided in anopposing relation to the boundary between the first driving electrode 3and the second driving electrode 4, and has a height several to severaltens times the diameter of the migratory particles 6. Thus, the barrier12 is featured in having a function to substantially inhibit thehorizontal migration of the migratory particles 6. When the migratoryparticles 6 are attracted onto the third driving electrode 5 after thewriting, the migratory particles can be prevented from migratinghorizontally by the presence of the barrier 12 even if the drivingvoltage applied to the third driving electrode 5 is lowered to reduceattraction forces toward the second substrate side. Accordingly, thebarrier 12 serves as a very effective means for achieving high-contrastdisplay at a relatively low voltage.

FIG. 11 shows another construction of the display device of the presentinvention wherein a charged film 13 is disposed on the surface of thethird driving electrode 5 arranged on the underside of the secondsubstrate 2, the charged film 13 having surface charges which areconstantly electrified with a polarity opposite to that of the chargedmigratory particles 6. The charged film 13 is preferably made of aferroelectric material or an electret material. In addition to theelectrostatic forces produced by the driving voltage and acting on themigratory particles 6 to attract them onto the third driving electrode5, electrostatic forces produced by the surface charges of the chargedfilm 13 also act to draw the migratory particles and prevent them frommigrating horizontally. Therefore, even when the driving voltage forproducing the electrostatic forces to attract the migratory particles 6toward the third driving electrode 5 is lowered, high-contrast displaycan be provided.

The third driving electrode 5 arranged on the underside of the secondsubstrate 2 is not always required to cover the entire pixel. In aconstruction shown in FIG. 12, for example, a third driving electrode 5having a cutout formed in its part opposing to the boundary between thefirst driving electrode 3 and the second driving electrode 4 is disposedon the underside of the second substrate 2 in the construction of FIG.1. The construction of FIG. 12 is advantageous in that the displaypattern is more surely transferred with the migration of the migratoryparticles 6 in the write operation in accordance with the addressingmethod described above with reference to FIGS. 4 and 5.

In the above description, one pair of the first driving electrode 3 andthe second driving electrode 4 is arranged in each pixel for the sake ofexplanation. However, the number of electrodes disposed in each pixel isnot limited to a particular value in the present invention, and as amatter of course plural pairs of electrodes may also be disposed in eachpixel. FIGS. 13A and 13B each show a construction in which two pairs ofelectrodes are disposed in each pixel. FIG. 13A corresponds to theconstruction of FIG. 1, and FIG. 13B corresponds to the construction ofFIG. 10.

(Materials and Manufacturing Methods of Components)

The method of manufacturing the display device of this embodiment willbe described below with reference to FIG. 1. First, the first drivingelectrodes 3 and the second driving electrodes 4 are formed andpatterned into predetermined shapes on the first substrate 1. Then, thethird driving electrodes 5 are likewise formed and patterned intopredetermined shapes on the second substrate 2. Each substrate may bemade of any of inorganic materials including polymer films such aspolyethylene terephthalate (PET) and polyether sulfone (PES), glass, andquartz. The driving electrode may be made of any material so long as itis capable of patterning. Materials of the transparent electrode may be,e.g., indium tin oxide (ITO).

The surface of the driving electrode may be colored by utilizing thecolor of an electrode material itself or the color of an insulatinglayer material itself formed on the electrode material, or by forming alayer of a material having a desired color on the electrode, theinsulating layer or the substrate surface. As an alternative, theinsulating layer, for example, may be mixed with a coloring material.

Subsequently, an insulating layer 8 is formed on both the first drivingelectrode 3 and the second driving electrode 4, and an insulating layer9 is formed on the third driving electrode 5. Materials of eachinsulating layer are preferably hard to produce pinholes in the form ofa thin film and have a low dielectric constant. Such materials include,for example, amorphous fluorocarbon resins, highly transparentpolyimides, and PET. A film thickness of the insulating layer ispreferably on the order of 100 nm to 1 μm.

Then, the partitions 10 are formed on the second substrate 2. A heightof each partition 10 is preferably not larger than 500 μm so thatflexibility is ensured. If the distance between the first substrate 1and the second substrate 2 is large, the transfer time of the displaypattern is prolonged and the driving voltage must be increased. From thepractical point of view, therefore, the partition height is preferablynot larger than 100 μm. Also, taking into account the diameter of themigratory particles 6, the partition height is preferably not smallerthan the particle diameter. Further, taking into account the migrationof the migratory particles between the first or second driving electrodeand the third driving electrode for transfer display, the partitionheight is preferably not smaller than twice the particle diameter.Moreover, in order that the migratory particles are less affected byelectric fields produced by the voltages applied to the first drivingelectrode and the second driving electrode in the non-selected line, thepartition height is preferably not smaller than five times the particlediameter.

The partitions 10 are not particularly limited in arrangement, but theyare preferably arranged to surround each pixel so that the migratoryparticles 6 will not migrate between the pixels. A polymer resin is usedas a material of the partitions 10. The partitions 10 may be formed inany suitable manner. For example, the partitions 10 are formed by amethod of coating a photosensitive resin layer and patterning the layerthrough the steps of exposure and wet development, or a method ofbonding partitions prepared separately, or a printing method.Alternatively, a method of forming partitions on the surface of thelight-transparent first substrate by molding is also usable.

Then, the transparent dielectric liquid 7 and the migratory particles 6are filled in each pixel space surrounded by the partitions 10. Acolorless transparent liquid, such as silicone oil, toluene, xylene,high-purity petroleum, is used as the dielectric liquid 7. The migratoryparticles 6 being black are made of a material that exhibits goodcharging characteristics in the dielectric liquid 7. Such a material is,e.g., a resin, such as polyethylene or polystyrene, mixed with carbon,etc. In consideration of the height of the partitions 10, the diameterof the migratory particles 6 is usually in the range of about 0.1 μm to10 μm.

Then, after forming an adhesive layer on a joint surface of the firstsubstrate 1 to the second substrate 2, the first and second substrates1, 2 are aligned with each other and bonded together under heating. Adisplay device is completed by connecting voltage applying means to thebonded assembly.

The barriers 12 on the second substrate 2, shown in FIG. 10, can beformed using a material and a method similar to those used for formingthe partitions 10. More specifically, a polymer resin is used as amaterial of the barriers 12. Further, the barriers 12 are formed by amethod of coating a photosensitive resin layer and patterning the layerthrough the steps of exposure and wet development, or a method ofbonding barriers prepared separately, or a printing method.Alternatively, a method of forming barriers on the surface of thelight-transparent second substrate by molding is also usable.

The charged film 13 on the second substrate 2, shown in FIG. 11, can bemade of any of ferroelectric materials and electret materials.

When ferroelectric materials are used, preferable examples of thematerials include inorganic compounds such as lead zirconate titanate(PZT), lead lanthanum-added zirconate titanate (PLZT) and bariumtitanate, and organic polymers such as polyvinylidene fluoride (PVDF)and a copolymer of vinylidene fluoride and trifluoroethylene(PVDF/PTrFE). In this case, the charged film 13 can be formed by, e.g.,the sol-gel process, the sputtering process or the CVD (Chemical VaporDeposition) process.

When electret materials are used, fluorocarbon resins such as Teflon(Teflon-FEP and Teflon-TFE) provide superior characteristics. Otherpreferable materials are, for example, polyethylene, polypropylene,polystyrene, polymethyl methacrylate, polyvinyl chloride, polyethyleneterephthalate, and polyimide. In this case, the charged film 13 can beformed by, e.g., the thermo-electret process, the electro-electretprocess, the radio-electret process, the photo-electret process, or themechano-electret process.

EXAMPLES

The present invention will be described in more detail in connectionwith Examples.

Example 1

In this Example, a (3×3)-matrix display cell having the cellconstruction shown in FIG. 1 was fabricated and operated in accordancewith the above-described Passive Matrix Addressing Method 1 to implementthe passive matrix addressing based on bi-directional writing. Thebi-directional writing is difficult to realize with the constructiondisclosed in the above-cited Japanese Patent Publication No. (by PCTapplication) 8-507154, and is one feature specific to the presentinvention. With this feature, the display cell of this Example is ableto perform the bi-directional writing, i.e., changes from a white toblack view and writing from a black to white view.

FIG. 14 is a plan view of the (3×3)-matrix display cell thus fabricated.The size of one pixel was 1 mm×1 mm, and the area ratio of the firstdriving electrode to the second driving electrode was 20:80.

A method of manufacturing the cell will be briefly described below withreference to FIGS. 1 and 14. First, an insulating layer 8 made of anacrylic resin containing a white pigment, such as alumina, dispersedtherein was formed on an overall surface of a first substrate 1 formedof a PET film having a thickness of 200 μm. Then, an ITO film was formedas a second driving electrode 4 on the insulating layer 8 at a lowtemperature and patterned into a shape as shown through the steps ofphotolithography and dry etching. Then, a deep-black titanium carbidefilm was formed as a first driving electrode 3 on the insulating layer 8and patterned in a similar manner. Then, another insulating layer 8 madeof an amorphous fluorocarbon resin was formed in a thickness of 200 nmon the overall surface.

Subsequently, an ITO film was formed as a third driving electrode 5 on asecond substrate 2 formed of a PET film at a low temperature andpatterned into a shape as shown. An insulating layer 9 made of anamorphous fluorocarbon resin was then formed in a thickness of 200 nm onthe overall surface. Partitions 10 were formed on the insulating layer9. The partitions 10 were formed in a height of 70 μm by coating aphotosensitive epoxy resin and patterning the coated resin through thesteps of exposure and wet development. A dielectric liquid 7 and blackcharged migratory particles 6 were filled in each space surrounded bythe formed partitions 10.

Silicone oil was used as the dielectric liquid 7. A mixture ofpolystyrene and carbon, having an average particle diameter of about 1μm, was used as the black charged migratory particles 6. The migratoryparticles 6 were positively charged in the silicone oil. Then, a patternof thermally fusing adhesive layer was formed on a joint surface of thefirst substrate 1 to the second substrate 2, and the first substrate 1was placed on the partitions 10 formed on the second substrate 2 whileproperly aligning both the substrates with each other. The first andsecond driving electrodes 3, 4 were then bonded together under heating.A display device was completed by connecting voltage applying circuits(not shown) to the bonded assembly.

The addressing method in this Example will be described below.

The first driving electrodes 3 were used as first data-signal electrodelines (D11-D13), the second driving electrodes 4 were used as seconddata-signal electrode lines (D21-D23), and the third driving electrodes5 were used as scan-signal electrode lines (S1-S3).

FIG. 15A is a time chart of driving voltages applied to the first andsecond data-signal electrode lines and the scan-signal electrode lines,and FIG. 15B shows a change of the display condition in each timeperiod. In FIGS. 15A and 15B, each time period (T1, T2 or T3) is set to90 msec. Further, a time period A represents a period in which themigratory particles are moved away from the third driving electrode, andis set to 30 msec. A time period B represents a period in which themigratory particles are horizontally migrated, and is set to 30 msec. Atime period C represents a period in which a display pattern istransferred onto the third driving electrode, and is set to 30 msec.

Since the bi-directional writing is possible, an initial operation toperform total reset is not required in this Example. It is assumed inthis Example that a pattern shown in a time period T0 is given as aninitial display pattern, and all pixels are reversed in displaycondition, i.e., color in view, for each of the scan-signal electrodelines (S1-S3). Note that writing of information was performed in thisExample in accordance with the Passive Matrix Addressing Method 1described above with reference to FIGS. 6 and 7. The detailed behaviorof the migratory particles in the write operation is similar to that inthe explanation of the Passive Matrix Addressing Method 1 and thereforeis not described herein.

The addressing method will now be described in sequence following thetime chart of FIG. 15A. In the time period T1, the driving voltages wereapplied to the respective lines in three stages. First, in the timeperiod A, Vd3=+60 V was applied to the scan-signal electrode line S1,which is selected at that time (i.e., a selected line), and Vd3=60 V wasapplied to the scan-signal electrode lines S2, S3, which are notselected at that time (i.e., non-selected lines). Also, 0 V was appliedto all of the first data-signal electrode lines (D11-D13) and all of thesecond data-signal electrode lines (D21-D23).

In the next time period B, as white-view writing voltages, Vd1=−30 V wasapplied to the first data-signal electrode lines D11, D13 correspondingto the pixels (1,1) and (1,3), and Vd2=+30 V was applied to the seconddata-signal electrode lines D21, D23 corresponding to them. Also, asblack-view writing voltages, Vd1=+30 V was applied to the firstdata-signal electrode line D12 corresponding to the pixel (1,2), andVd2=−30 V was applied to the second data-signal electrode line D22corresponding to the same. As a result, all pixels in the scan-signalelectrode line S1 as the selected line were rewritten and reversed indisplay condition.

Then, in the time period C, Vd3=−60 V was applied to the scan-signalelectrode line S1 as the selected line for transferring the rewrittendisplay pattern onto the second substrate. During the time period T1,each of the pixels in the scan-signal electrode lines S2, S3 as thenon-selected lines was maintained in the initial display condition.

Subsequently, the addressing was successively performed in the timeperiods T2 and T3 in a similar manner according to a selected pixelpattern. As a result, an objective reversed display pattern was obtainedwith a high contrast. A deterioration of contrast due to crosstalk andfailures in the migration and holding of the migratory particles was notobserved in the obtained display. An average contrast ratio of whiteview to black view was as high as about 10:1.

Comparative Example 1

As Comparative Example 1, a (3×3)-matrix display cell having the cellconstruction, shown in FIG. 17A, as disclosed in the above-citedJapanese Patent Publication No. (by PCT application) 8-507154 wasfabricated and operated in accordance with the passive matrix addressingbased on unidirectional writing.

FIG. 24 is a plan view of the (3×3)-matrix display cell thus fabricated.The size of one pixel was 1 mm×1 mm, and the area ratio of the firstdriving electrode 3 to the second driving electrode 4 was 35:65. Thespacing between the first substrate and the second substrate was 70 μmand the height of the step 15 was 0.3 μm. Positively charged migratoryparticles having an average particle diameter of 1 μm were used. Thedriving electrodes and the migratory particles were colored in the samemanner as made in the construction of FIG. 1.

A method of manufacturing the cell will be briefly described below withreference to FIGS. 17A and 24. First, an insulating layer 8 made of anacrylic resin containing a white pigment, such as alumina, dispersedtherein was formed on an overall surface of a first substrate 1 formedof a PET film having a thickness of 200 μm. Then, a deep-black titaniumcarbide film was formed as a first driving electrode 3 on the insulatinglayer 8 and patterned into a shape as shown through the steps ofphotolithography and dry etching.

Then, an epoxy resin film was coated in a thickness of 0.3 μm, and insuccession an ITO thin film was formed as a second driving electrode 4at a low temperature by magnetron sputtering. Subsequently, a resistfilm was coated and patterned into a shape as shown. Finally, the firstsubstrate 1 was subjected to reactive dry etching using CF₄ and O₂gases. As a result, a structural member having the second drivingelectrodes 4 arranged on the steps 15 with the height of 0.3 μm wasfabricated. Thereafter, another insulating layer 8 made of an amorphousfluorocarbon resin was formed in a thickness of 200 nm on the overallsurface.

Subsequently, an ITO film was formed as a control driving electrode 14on a second substrate 2 formed of a PET film at a low temperature andpatterned into a shape as shown. An insulating layer 9 made of anamorphous fluorocarbon resin was then formed in a thickness of 200 nm onthe overall surface. Partitions 10 were formed on the insulating layer9. The partitions 10 were formed in a height of 70 μm by coating aphotosensitive epoxy resin and patterning the coated resin through thesteps of exposure and wet development. A dielectric liquid 7 and blackcharged migratory particles 6 were filled in each space surrounded bythe formed partitions 10.

The subsequent process is exactly the same as those described above inExample 1, and hence a description thereof is omitted herein.

The addressing method in Comparative Example 1 will be described below.

The first driving electrodes 3 were used as scan-signal electrode lines(S1-S3), and the control electrodes 14 were used as data-signalelectrode lines (D11-D13). The second driving electrodes 4 were used ascommon electrodes and fixedly maintained at the ground potential.

FIG. 25A is a time chart of driving pulses applied to the scan-signalelectrode lines and the data-signal electrode lines, and FIG. 25B showsa change of the display condition in each time period. In FIGS. 25A and25B, each time period is set to 50 msec.

The addressing operation of the cell was started by initially resettingan overall screen to a white view. Then, in each of the scan-signalelectrode lines, writing was performed in one direction (i.e., from awhite to a black view) for selected pixels (1,2), (2,1) (2,3) and (3,2)corresponding to a set display pattern. Note that writing of informationwas performed in this Comparative Example 1 in accordance with theaddressing method described above with reference to FIGS. 18 to 21. Thedetailed behavior of the migratory particles in the write operation issimilar to that in the explanation of the addressing method describedabove with reference to FIGS. 18 to 21, and therefore is not describedherein.

The addressing method will now be described in sequence following thetime chart of FIG. 25A. In a time period TR, Vd=−50 V was applied to allof the scan-signal electrode lines S1 to S3, and Vc=0 V was applied toall of the data-signal electrode lines D1-D3, thereby resetting all thepixels to provide a white view.

Then, in a time period T1, Vd=+50 V was applied to the scan-signalelectrode line S1, which is selected at that time (i.e., a selectedline), and Vd=+5 V was applied to the scan-signal electrode lines S2,S3, which are not selected at that time (i.e., non-selected lines). Atthe same time, the control voltage Vc=+50 V was applied to thedata-signal electrode line D2 corresponding to the selected pixel (1,2),and Vc=+250 V was applied to the data-signal electrode lines D1, D3corresponding to the non-selected pixels (1,1), (1,3). As a result, onlythe selected pixel (1,2) in the selected scan-signal electrode line S1was rewritten to provide a black view, while a white view was maintainedin the non-selected pixels (1,1), (1,3) in the selected scan-signalelectrode line S1 and each of the pixels in the non-selected scan-signalelectrode lines S2, S3. In the non-selected pixels (1,1) and (1,3),however, the migratory particles were not sufficiently held down evenunder Vc=+250 V and part of the migratory particles was migrated to theside of the second driving electrode as shown in FIG. 22C. Hence, thenon-selected pixels (1,1) and (1,3) presented not a white view, but agray view as shown in FIG. 25B.

Subsequently, the addressing was successively performed in time periodsT2 and T3 in a similar manner according to a selected pixel pattern. Asa result, an objective display pattern was obtained, but a white viewwas entirely grayish and the display contrast was poor. An averagecontrast ratio of white view to black view was about 3:1.

Example 2

In this Example 2, the (3×3)-matrix display cell employed in aboveExample 1 was operated in accordance with the above-described PassiveMatrix Addressing Method 2 to implement the passive matrix addressingbased on bi-directional writing.

A display cell used in this Example has exactly the same construction asthat used in above Example 1 (plan view being shown in FIG. 14), andtherefore an explanation of the manufacturing process is omitted herein.

The addressing method in this Example will be described below.

As with above Example 1, the first driving electrodes 3 were used asfirst data-signal electrode lines (D11-D13), the second drivingelectrodes 4 were used as second data-signal electrode lines (D21-D23),and the third driving electrodes 5 were used as scan-signal electrodelines (S1-S3).

FIG. 16A is a time chart of driving voltages applied to the first andsecond data-signal electrode lines and the scan-signal electrode lines,and FIG. 16B shows a change of the display condition in each timeperiod. In FIGS. 16A and 16B, each time period (T1, T2 or T3) is set to60 msec. Further, a time period A represents a period in which themigratory particles are moved away from the third driving electrode andmigrated onto the first or second driving electrode, and is set to 30msec. A time period B represents a period in which a display pattern istransferred onto the third driving electrode, and is set to 30 msec.

As with above Example 1, since the bi-directional writing is possible,an initial operation to perform total reset is not required in thisExample. Also, it is assumed that a pattern shown in a time period T0 isgiven as an initial display pattern, and all pixels are reversed indisplay condition, i.e., color in view, for each of the scan-signalelectrode lines (S1-S3). Note that writing of information was performedin this Example in accordance with the Passive Matrix Addressing Method2 described above with reference to FIGS. 8 and 9. The detailed behaviorof the migratory particles in the write operation is similar to that inthe explanation of the Passive Matrix Addressing Method 2 and thereforeis not described herein.

The addressing method will now be described in sequence following thetime chart of FIG. 16A. In the time period T1, the driving voltages wereapplied to the respective lines in two stages. In the first-half timeperiod A, Vd3=+60 V was applied to the selected scan-signal electrodeline S1, and Vd3=−60 V was applied to the non-selected scan-signalelectrode lines S2, S3. At the same time, as white-view writingvoltages, Vd1=−30 V was applied to the first data-signal electrode linesD11, D13 corresponding to the pixels (1,1) and (1,3), and Vd2=+30 V wasapplied to the second data-signal electrode lines D21, D23 correspondingto them. Also, as black-view writing voltages, Vd1=+30 V was applied tothe first data-signal electrode line D12 corresponding to the pixel(1,2), and Vd2=−30 V was applied to the second data-signal electrodeline D22 corresponding to the same. As a result, all pixels in theselected scan-signal electrode line S1 were rewritten and reversed indisplay condition. Then, in the latter-half time period B, Vd3=−60 V wasapplied to the selected scan-signal electrode line S1 for transferringthe rewritten display pattern onto the third driving electrode 5. Duringthe time period T1, each of the pixels in the non-selected scan-signalelectrode lines S2, S3 was maintained in the initial display condition.

Subsequently, the addressing was successively performed in the timeperiods T2 and T3 in a similar manner according to a selected pixelpattern. As a result, an objective reversed display pattern was obtainedwith a high contrast, and the objective pattern was displayed in ashorter time than required in above Example 1. A deterioration ofcontrast due to crosstalk and failures in the migration and holding ofthe migratory particles was not observed in the obtained display. Anaverage contrast ratio of white view to black view was as high as about10:1.

Example 3

In this Example 3, a (3×3)-matrix display cell having the cellconstruction shown in FIG. 10, wherein the barriers 12 were provided onthe surfaces of the third driving electrodes 5 arranged on the undersideof the second substrate 2, was fabricated and operated with the passivematrix addressing based on bi-directional writing.

A plan view of the (3×3)-matrix display cell thus fabricated was thesame as that shown in FIG. 14. As with above Example 1, the size of onepixel was 1 mm×1 mm, and the area ratio of the first driving electrode 3to the second driving electrode 4 was 20:80.

A method of manufacturing the cell will be briefly described below withreference to FIGS. 10 and 14.

First, an insulating layer 8 made of an acrylic resin containing a whitepigment, such as alumina, dispersed therein was formed on an overallsurface of a first substrate 1 formed of a PET film having a thicknessof 200 μm. Then, an ITO film was formed as a second driving electrode 4on the insulating layer 8 at a low temperature and patterned into ashape as shown through the steps of photolithography and dry etching.Then, a deep-black titanium carbide film was formed as a first drivingelectrode 3 on the insulating layer 8 and patterned in a similar manner.Then, another insulating layer 8 made of an amorphous fluorocarbon resinwas formed in a thickness of 200 nm on the overall surface. Partitions10 were formed on this insulating layer 8. The partitions 10 were formedin a height of 70 μm by coating a photosensitive epoxy resin andpatterning the coated resin through the steps of exposure and wetdevelopment. A dielectric liquid 7 and black charged migratory particles6 were filled in each space surrounded by the formed partitions 10.

Subsequently, an ITO film was formed as a third driving electrode 5 on asecond substrate 2 formed of a PET film at a low temperature andpatterned into a shape as shown. An insulating layer 9 made of anamorphous fluorocarbon resin was then formed in a thickness of 200 nm onthe overall surface. Barriers 12 were then formed in a thickness of 30μm on the insulating layer 9 through the steps of coating, exposing anddeveloping a photosensitive epoxy resin.

The subsequent process is exactly the same as those described above inExample 1, and hence a description thereof is omitted herein.

Matrix addressing was performed exactly in the same manner as that inExample 1. As a result, an objective display pattern was obtained with ahigher contrast because of the presence of the barriers 12. Further, thedriving voltage applied for transferring the display pattern onto thethird driving electrode could be reduced to Vd3=−45 V. A deteriorationof contrast due to crosstalk and failures in the migration and holdingof the migratory particles was not observed in the obtained display. Anaverage contrast ratio of white view to black view was as high as about15:1.

Example 4

In this Example 4, a (3×3)-matrix display cell having the cellconstruction shown in FIG. 11, wherein the charged film 13 was formed onthe surfaces of the third driving electrodes 5 arranged on the undersideof the second substrate 2, was fabricated and operated with the passivematrix addressing based on bi-directional writing.

A plan view of the (3×3)-matrix display cell thus fabricated was thesame as that shown in FIG. 14. As with above Example 1, the size of onepixel was 1 mm×1 mm, and the area ratio of the first driving electrode 3to the second driving electrode 4 was 20:80.

A method of manufacturing the cell will be briefly described below withreference to FIGS. 11 and 14.

First, an insulating layer 8 made of an acrylic resin containing a whitepigment, such as alumina, dispersed therein was formed on an overallsurface of a first substrate 1 formed of a PET film having a thicknessof 200 μm. Then, an ITO film was formed as a second driving electrode 4on the insulating layer 8 at a low temperature and patterned into ashape as shown through the steps of photolithography and dry etching.Then, a deep-black titanium carbide film was formed as a first drivingelectrode 3 on the insulating layer 8 and patterned in a similar manner.Then, another insulating layer 8 made of an amorphous fluorocarbon resinwas formed in a thickness of 200 nm on the overall surface. Partitions10 were formed on this insulating layer 8. The partitions 10 were formedin a height of 70 μm by coating a photosensitive epoxy resin andpatterning the coated resin through the steps of exposure and wetdevelopment. A dielectric liquid 7 and black charged migratory particles6 were filled in each space surrounded by the formed partitions 10.

Subsequently, an ITO film was formed as a third driving electrode 5 on asecond substrate 2 formed of a PET film at a low temperature andpatterned into a shape as shown. An insulating layer 9 made of anamorphous fluorocarbon resin was then formed in a thickness of 200 nm onthe overall surface.

The charged film 13 was then formed. Teflon-FEP was used as a materialof the charged film 13, and was treated to have an electret propertywith a corona discharge under heating at a high temperature. Morespecifically, the insulating layer 9 was etched by Ar gas for fiveminutes, whereby the layer surface was roughed to increase adhesion ofthe charged film onto it. After laying a transparent Teflon-FEP sheethaving a thickness of 5 μm on the roughed surface, the sheet was heatedand fused at 300° C. while a weight was imposed on the sheet through aglass plate. Then, by cooling the sheet, a Teflon-FEP film was formed ina thickness of 5 μm on the third driving electrode 5. For treatment togive the Teflon-FEP sheet an electret property, a knife edge electrodeattached to an XYZ displacement mechanism and the second substrate,including the Teflon-FEP film and the electrode films formed thereon,were both placed in a thermostatic chamber. The knife edge electrode wasarranged to face a surface of the Teflon-FEP film through a gap, and thedistance (gap) between the knife edge electrode and the Teflon-FEP filmwas adjusted to 200 μm. While maintaining an inner space of thethermostatic chamber at 300° C., a voltage of 5 kV was applied betweenthe electrode films and the knife edge electrode in such a directionthat the knife edge electrode was on the negative side, therebygenerating a corona discharge between the electrode films and the knifeedge electrode. The knife edge electrode was moved to reciprocate at aconstant speed in a horizontal direction parallel to the substratesurface by the XYZ displacement mechanism supporting the knife edgeelectrode. The overall substrate surface was thereby subjected touniform irradiation of the corona discharge. The treatment to give theTeflon-FEP sheet an electret property was completed by rapidly coolingthe irradiated substrate surface by dry nitrogen. The charged film thusobtained was transparent and a measured surface potential of the chargedfilm was −20 V.

The subsequent process is exactly the same as those described above inExample 1, and hence a description thereof is omitted herein.

Matrix addressing was performed exactly in the same manner as that inExample 1. As a result, an objective display pattern was achieved in anaddressing time comparable to that in Example 1. In other words, it wasconfirmed that the addressing characteristics were hardly affected byattraction of the migratory particles by the charged film 13. Further,the objective display pattern was obtained with a higher contrastbecause of the presence of the charged film 13. In addition, the drivingvoltage applied for transferring the display pattern onto the thirddriving electrode could be reduced to Vd3=−40 V. A deterioration ofcontrast due to crosstalk and failures in the migration and holding ofthe migratory particles was not observed in the obtained display. Anaverage contrast ratio of white view to black view was as high as about13:1.

Example 5

In this Example 5, a cell having the construction shown in FIG. 3 wasfabricated and operated to provide color display by forming red, greenand blue pixels on the first substrate 1 in a combined arrangement. Thesize of one pixel was 1 mm×1 mm, and the area ratio of the first drivingelectrode 3 to the second driving electrode 4 was 20:80.

A method of manufacturing a red cell will be briefly described belowwith reference to FIG. 3A.

First, a colored insulating layer 11 made of an acrylic resin containinga red pigment dispersed therein was formed on a first substrate 1 formedof a PET film having a thickness of 200 μm. Then, a deep-black titaniumcarbide film was formed as a first driving electrode 3 on the insulatinglayer 11 and patterned into a shape as shown through the steps ofphotolithography and dry etching.

Then, an amorphous fluorocarbon resin was coated in a thickness of 100nm, and in succession an ITO thin film was formed as a second drivingelectrode 4 at a low temperature by magnetron sputtering. Subsequently,a resist film was coated and patterned into a shape as shown. Finally,the first substrate 1 was subjected to reactive dry etching using CF₄and O₂ gases, whereby the second driving electrode 4 of ITO was formed.Thereafter, an insulating layer 8 made of an amorphous fluorocarbonresin was formed in a thickness of 200 nm on the overall surface.

The subsequent process is exactly the same as those described above inExample 1, and hence a description thereof is omitted herein.

The red cell thus fabricated was operated to provide display inaccordance with the method described above in connection with FIGS. 4and 5. First, the driving voltage Vd1=−30 V was applied to the firstdriving electrode 3 and the driving voltage Vd2=+30 V was applied to thesecond driving electrode 4 for migrating the migratory particles 6 so asto position on the side of the first driving electrode 3. Then, thedriving voltage Vd3=−60 V was applied to the third driving electrode 5,causing the migratory particles 6 to be attracted onto the third drivingelectrode 5 by electrostatic forces. At this time, when looking at thecell from the second substrate side, the cell presented a red viewbecause the red colored insulating layer 11 formed under the transparentsecond driving electrode 4 was observed by the viewer.

Subsequently, the display condition was rewritten in accordance with thePassive Matrix Addressing Method 1. The driving voltages Vd1=Vd2=0 Vwere applied to the first and second driving electrodes 3, 4 and thedriving voltage Vd3=+60 V was applied to the third driving electrode 5,whereby the migratory particles 6 were migrated away from the secondsubstrate 2 toward the first substrate side. Thereafter, the drivingvoltage Vd1=+30 V was applied to the first driving electrode 3 and thedriving voltage Vd2=−30 V was applied to the second driving electrode 4for migrating the migratory particles 6 so as to position on the side ofthe second driving electrode 4. Then, the driving voltage Vd3=−60 V wasapplied again to the third driving electrode 5, causing the migratoryparticles 6 to be transferred onto the second substrate side. At thistime, the cell presented a black view because the black migratoryparticles 6 and the deep-black first driving electrode 3 were observedfrom the second substrate side. The display condition could be rewrittenin a time of not longer than 50 msec.

Successively, the display condition was rewritten in accordance with thePassive Matrix Addressing Method 2. The driving voltage Vd3=+60 V wasapplied to the third driving electrode 5 for migrating the migratoryparticles 6 away from the second substrate 2 toward the first substrateside. Simultaneously, the driving voltage Vd1=−30 V was applied to thefirst driving electrode 3 and the driving voltage Vd2=+30 V was appliedto the second driving electrode 4 for migrating the migratory particles6 so as to position on the side of the first driving electrode 3. Then,the driving voltage Vd3=−60 V was applied to the third driving electrode5, causing the migratory particles 6 to be transferred onto the secondsubstrate side. At this time, the cell presented a red view because thered colored insulating layer 11 formed under the transparent seconddriving electrode 4 was observed from the second substrate side. Thedisplay condition could be rewritten in a time of not longer than 30msec, and the rewrite speed was increased in comparison with the case ofusing the Passive Matrix Addressing Method 1.

A green cell was fabricated through the same process as for the red cellexcept for forming, on a first substrate 1 formed of a PET film, acolored insulating layer 11 made of an acrylic resin containing a greenpigment dispersed therein. The green cell thus fabricated was operatedto provide display in accordance with the same method as for the redcell. As a result, the green cell was able to present a green view asintended.

A blue cell was also fabricated through the same process as for the redcell except for forming, on a first substrate 1 formed of a PET film, acolored insulating layer 11 made of an acrylic resin containing a bluepigment dispersed therein. The blue cell thus fabricated was operated toprovide display in accordance with the same method as for the red cell.As a result, the blue cell was able to present a blue view as intended.

Three types of cells representing red, green and blue pixels werefabricated in a combined arrangement by forming the colored insulatinglayer 11 in three colors of red, green and blue. As a result, colordisplay was obtained by those cells. In other words, color display couldbe realized by fabricating three cells each having the construction ofFIG. 3A to provide red, green and blue pixels, and arranging those threepixels adjacent to each other so as to provide one composite pixel.

As described above in detail, the present invention can provide thefollowing advantages.

First, in the selected line, the migratory particles forming a displaypattern are attracted onto the third driving electrode, and are keptaway from the first and second driving electrodes. Therefore, even whenthe driving voltages applied to the first and second driving electrodesare changed, the migratory particles are less affected by the change ofan electric field, and the display pattern is avoided from changing dueto the unintended migration of the migratory particles. It is thuspossible to surely inhibit the unintended migration of the migratoryparticles and hold them in a desired position under a lower voltage.

Secondly, in an electrophoretic display device of the horizontallymigrating type, passive matrix addressing is realized with a highdisplay contrast without causing any crosstalk. The reason is that thenovel addressing method has succeeded in substantially perfectlyeliminating the occurrence of crosstalk, which has been experienced inthe conventional device due to a failure in holding the migratoryparticles properly in the non-selected pixels.

Thirdly, bi-directional writing is enabled in the present invention.Therefore, initial total reset is no longer required, and partialrewriting to rewrite only part of a display screen is realized.

Fourthly, by forming the barriers or the charged film, the drivingvoltage can be further reduced which is required for inhibiting themigration of the migratory particles and holding them at a standstill ina state where the display pattern is transferred onto the third drivingelectrode. In addition, the contrast is improved.

Fifthly, color display can be realized.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. An electrophoretic display method for use in anelectrophoretic display device comprising a first substrate, first andsecond driving electrodes arranged on the first substrate, a secondsubstrate arranged in an opposing relation to the first substrate, athird driving electrode arranged on the second substrate, a transparentdielectric liquid filled between the first substrate and the secondsubstrate, and a plurality of migratory particles dispersed in thetransparent dielectric liquid, the method comprising the steps of:migrating the migratory particles onto the first driving electrode orthe second driving electrode to provide a desired view state; andtransferring the migratory particles on the first driving electrode andthe second driving electrode onto corresponding areas of the secondsubstrate opposing the first driving electrode and the second drivingelectrode, respectively.
 2. An electrophoretic display method accordingto claim 1, further comprising the step of applying voltages to thefirst driving electrode, the second driving electrode and the thirddriving electrode to provide a time period in which a relationship ofpotentials of the first driving electrode and the second drivingelectrode being higher than a potential of the third driving electrodeis satisfied for positively charged migratory particles, or a timeperiod in which a relationship of potentials of the first drivingelectrode and the second driving electrode being lower than a potentialof the third driving electrode is satisfied for negatively chargedmigratory particles, whereby the migratory particles are attracted ontothe third driving electrode arranged on the second substrate.
 3. Anelectrophoretic display method according to claim 1, further comprisingthe step of rewriting a display through a first stage of moving themigratory particles, which are attracted to the third driving electrode,away from the third driving electrode, a second stage of migrating themigratory particles between the first driving electrode and the seconddriving electrode, and a third stage of attracting the migratoryparticles onto the third driving electrode.
 4. An electrophoreticdisplay method according to claim 1, further comprising the step ofapplying voltages to the first driving electrode, the second drivingelectrode and the third driving electrode to provide a time period inwhich a relationship of potentials of the first driving electrode andthe second driving electrode being lower than a potential of the thirddriving electrode is satisfied for positively charged migratoryparticles, or a time period in which a relationship of potentials of thefirst driving electrode and the second driving electrode being higherthan a potential of the third driving electrode is satisfied fornegatively charged migratory particles, whereby the migratory particlesare moved away from the third driving electrode arranged on the secondsubstrate.
 5. An electrophoretic display method for use in anelectrophoretic display device comprising a first substrate, first andsecond driving electrodes arranged on the first substrate, a secondsubstrate arranged in an opposing relation to the first substrate, athird driving electrode arranged on the second substrate, a transparentdielectric liquid filled between the first substrate and the secondsubstrate, and a plurality of migratory particles dispersed in thetransparent dielectric liquid, the method comprising the steps of;migrating the migratory particles between the first driving electrodeand the second driving electrode; migrating the migratory particlesbetween the first driving electrode or the second driving electrode andthe third driving electrode; and rewriting display through a first stageof moving the migratory particles, which are attracted onto the thirddriving electrode, away from the third driving electrode, andsimultaneously migrating the migratory particles onto the first drivingelectrode or the second driving electrode, and a second stage ofattracting the migratory particles to the second substrate side.